1. Field Of The Invention
This invention relates to an improved method for the production of 1,4-butanediol. More particularly, this invention relates to a method for converting a maleic acid-containing mixture to a substantially anhydrous mixture comprising 1,4-butanediol which is thereafter recovered from the mixture in high purity.
2. Description Of The Prior Art
1,4-Butanediol is a monomer used in the production of polybutylene terephthalate, a unique engineering plastic. Butanediol has been manufactured commercially by processes involving the Reppe reaction of acetylene and formaldehyde followed by hydrogenation of the reaction mixture. Other processes for the production of 1,4-butanediol involve the hydrolysis of dichlorobutanes or the hydrogenation of maleic anhydride.
Processes for the production of esters from maleic acid or maleic anhydride generally involve the acid catalyzed esterification of the maleic precursor to a dialkyl ester. Such processes suffer from the disadvantage that the acidic catalysts are difficult to remove from the product and even small amounts of acid in the ester product make it unsuitable for use in catalytic processes for hydrogenating the ester to 1,4-butanediol.
Processes for the production of maleic acid or maleic anhydride generally involve the high temperature, catalytic oxidation of hydrocarbons, e.g., benzene, to form an effluent gas comprising maleic acid and maleic anhydride. Such effluent gases from the reaction zone are generally quenched or scrubbed with water thereby forming an aqueous solution comprising maleic acid. Maleic acid or maleic anhydride is thereafter recovered from this aqueous maleic acid solution by a number of processing steps involving distillation, crystallization, and the like.
It is an object of the instant invention to provide a process for the conversion of maleic acid into its dialkyl esters without requiring the use of an esterification catalyst. It is also an object of this invention to provide a process for the production of dialkyl esters of maleic and fumaric acid which process does not require the use of high purity maleic acid or maleic anhydride. Finally, it is an object of this invention to provide a process for the production of dialkyl esters of maleic acid which employs crude aqueous maleic acid-containing mixtures such as those obtained in commercial processes for the production of maleic acid or maleic anhydride without the prior recovery and purification of the maleic acid or maleic anhydride.